如何激活机体的免疫系统，阻断负向免疫调控分子的信号转导是肿瘤免疫研究的热点。Calpain作为细胞内的蛋白酶，以往的研究认为其主要在胞内中发挥生理性调节作用，而对胞外Calpain的功能知之甚少。我们前期研究首次显示胞外Calpain1对T细胞的增殖和杀伤效能具有显著抑制作用，并且能促进T细胞表面抑制性分子PD-1的表达。据此，我们提出科学问题： Calpain是否为肿瘤微环境中独立的T细胞抑制分子？其抑制效应是否通过激活下游PD-1/PDL-1通路起作用？本研究将通过分析Calpain胞外表达与临床预后的关系；利用体内过继免疫模型和小鼠黑色素瘤模型确立Calpain抑制T细胞效能的作用；通过检测PD-1甲基化位点的变化和PD-1KO鼠模型研究Calpain促进PD-1/PDL-1通路活化的作用机制，为开发以该分子为核心的肿瘤免疫治疗提供理论依据。

How to activate the immune system and block the negative signal transduction is a currently needed to be solved problem in the study of tumor immunotherapy. Calpain is a family of calcium-dependent intracellular cysteine proteases with a wide range of substrates including various cell skeletal proteins and enzymes involved in intracellular signal transduction. Previous studies showed that calpain mainly plays physiological roles in cytoplasm, while its extracellular function is poorly understood. Our previous study showed a significant inhibitory effect of extracellular calpain1 on proliferation of T lymphocytes and activation. Calpain1 increased the expression of inhibitory molecules PD-1 on the surface of T cells. Accordingly, we put forward the scientific question: whether the calpain is an independent inhibitory molecule in tumor microenvironment? Does its inhibitory effect play an important role in the activation of the downstream PD-1/PDL-1 pathway? In this study, we will analyze the relationship between extracellular expression of calpain and clinical prognosis; we will study the mechanism of calpain on T cell proliferation and killing efficiency with Adoptive transfer model and mouse melanoma model in vivo; through detection of PD-1 methylation in T cell surface in vitro and PD-1KO mice study in vivo, we will investigate the effect of calpain on the PD-1/PDL-1 pathway. All these works would be helpful for providing theoretical basis for the development of tumor immunotherapy.